Soil physical properties form the foundation for understanding soil behaviour, water movement, nutrient retention and plant growth in irrigated agriculture. This chapter introduces soil as a heterogeneous, polyphasic and porous system consisting of solid, liquid and gaseous phases. It explains soil composition, texture, textural classes and mechanical analysis, with emphasis on the relative proportions of sand, silt and clay. The chapter also discusses specific surface area and its influence on water retention, nutrient exchange and other soil processes. Soil structure, including its type, class and grade, is examined along with the factors responsible for aggregate formation and stability. Particular attention is given to bulk density, pore space, macro- and micropores, soil aeration and infiltration. The agricultural significance of soil structure is related to soil tilth, root penetration, water and nutrient availability. The chapter further considers management practices, including tillage and methods for maintaining favourable physical conditions in irrigated soils.

Microbiology is the scientific study of microorganisms, including bacteria, fungi, algae, protozoa and viruses, and their interactions with plants, animals and the environment. Microorganisms are microscopic in size but have enormous importance in agriculture, food production, environmental management and biotechnology. In agricultural systems, microorganisms contribute to decomposition of organic residues, nutrient cycling, soil fertility, plant growth and suppression of harmful organisms. Beneficial microorganisms also form associations with plant roots and improve nutrient availability and plant health. At the same time, certain microorganisms cause plant diseases, food spoilage and environmental contamination. Agricultural microbiology applies the principles of general microbiology to understand these beneficial and harmful activities in farming systems. This chapter introduces the scope and importance of microbiology, major groups of microorganisms, basic laboratory concepts and their applications in agriculture. An understanding of microbial structure, metabolism, diversity and ecological functions provides the foundation for studying soil microbiology, plant–microbe interactions, biotechnology and environmental remediation.

Soil structure is highly important for maintaining favourable conditions for water movement, aeration, root development and crop production. In irrigated agriculture, inappropriate management practices can cause structural degradation through compression, puddling, compaction and crust formation. This chapter examines the major processes responsible for deterioration of soil structure and their effects on soil physical properties and crop performance. Soil compaction is discussed in relation to agricultural machinery, pressure distribution, formation of compacted layers and restrictions to root growth and water movement. The chapter also explains soil crusting, its mechanisms, effects on seedling emergence and methods for evaluating crust strength. Slow-permeable soils, including Regur soils, highly permeable soils and soils with shallow water tables are considered from a management perspective. Appropriate management practices are emphasized to restore permeability, improve soil structure and maintain favourable soil-water relationships. The chapter provides an integrated understanding of structural degradation and its management for sustainable irrigated agricultur

Soil chemical properties determine the availability, retention and movement of nutrients and strongly influence plant growth under irrigated conditions. This chapter introduces the fundamental chemical characteristics of soils, with particular emphasis on exchangeable bases, cation exchange and anion exchange. Cation exchange capacity (CEC) is discussed as an important indicator of the soil's capacity to retain and exchange nutrient cations. The chapter explains the principles and reactions involved in cation exchange, cation selectivity and the determination and expression of CEC. Relationships between CEC, soil pH and particle size are also considered, together with the concept of base saturation. These properties are important for understanding nutrient availability and fertilizer management in different soil types. The chapter further introduces the mechanism of nutrient uptake by plant roots, linking soil chemical reactions with plant nutrition. Understanding these processes provides an essential basis for managing soil fertility, improving nutrient-use efficiency and maintaining productive irrigated soils.

Soil organic matter is a key component of soil fertility, biological activity, aggregation and carbon storage. This chapter examines the origin, transformation and management of organic matter in agricultural soils, with particular attention to irrigated agroecosystems. It discusses the decomposition of organic matter under aerobic and anaerobic conditions and explains the major factors influencing decomposition rates. Microbial activity plays an important role in transforming organic materials and regulating nutrient cycling within the soil. The chapter introduces humus, humic substances and non-humic substances and explains interactions between clay and humus that influence soil properties. The relationship between soil organic matter and plant growth is also considered, highlighting its contribution to nutrient availability, soil structure and biological processes. Methods for maintaining soil organic matter and conserving soil carbon in agroecosystems are discussed along with factors controlling soil carbon levels. The chapter therefore establishes the importance of organic matter management for improving soil health, carbon conservation and the long-term sustainability of irrigated agricultural systems.

Water is one of the most important resources governing crop production in irrigated agriculture, and its behaviour within soil determines the availability of water to plants. This chapter presents the fundamental relationship between soil and water, beginning with the importance of soil water in crop production and the classification of soil water. Soil moisture constants and methods for measuring soil moisture content are discussed to explain the different forms and availability of water in the soil profile. The chapter introduces the potential concept of soil water and the components contributing to total soil water potential, including potential energy. Available water capacity is examined in relation to plant water supply, while capillarity and water retention explain how soil texture and pore characteristics influence water storage. The soil-water characteristic curve provides a basis for understanding changes in water content with soil-water potential. Soil-water hysteresis is also discussed to explain differences in wetting and drying behaviour. These concepts provide an essential foundation for efficient irrigation, crop water management and sustainable use of soil water resources

The movement of water through soil is fundamental to irrigation efficiency, drainage, nutrient transport and plant water availability. This chapter examines the principles governing water movement in both saturated and unsaturated soil conditions. It introduces the movement of water through the soil profile and discusses saturated hydraulic conductivity as an important parameter describing the ability of soil to transmit water. Water flow under unsaturated conditions is considered in greater detail, including the relationship between soil-water content and hydraulic conductivity. The chapter presents the equation for unsaturated flow and describes experimental approaches for studying water movement. Unsaturated hydraulic conductivity, represented as K(θ), provides an important basis for understanding the changing ability of soil to transmit water as soil moisture conditions vary. The chapter also considers prediction of soil-water flux, linking theoretical concepts with practical irrigation and soil-water management. Understanding water movement helps in determining irrigation requirements, reducing water losses, improving drainage and maintaining favourable soil-water conditions for crop growth.

The soil–plant relationship is central to crop productivity because soil conditions directly influence root development, water uptake, nutrient availability and plant growth. This chapter focuses particularly on the problems associated with salt-affected soils, including saline, sodic and acid soils. It explains the formation, distribution and characteristics of saline soils and describes the production constraints created by salinity stress. The effects of salinity on plant growth, evaluation of saline soils, reclamation and leaching are discussed together with leaching requirements and crop salt tolerance. Water and nutrient management strategies for saline soils, including the use of biofertilizers, are considered. Sodic soils are examined through their formation, characteristics, exchangeable sodium percentage (ESP) and sodium adsorption ratio (SAR), followed by reclamation practices and amendment use, particularly gypsum. The chapter also addresses acid soils, their formation, chemical characteristics, nutrient availability, plant-growth constraints and amelioration through liming. Calcareous soils and their management are also included, providing a comprehensive treatment of problematic soils affecting soil–plant interactions

Nitrogen is an essential plant nutrient and plays a particularly important role in intensively cultivated irrigated systems. This chapter examines nitrogen management in irrigated soils, where assured water availability and intensive cropping can increase nitrogen demand and create significant nutrient losses. The chapter begins with the functions of nitrogen and the forms in which nitrogen occurs in soil, including inorganic and organic forms. Mineralization and immobilization processes are discussed, along with factors affecting nitrogen mineralization and nitrogen transformations under waterlogged conditions. Major pathways of nitrogen loss, particularly volatilization, denitrification and leaching, are examined because they directly influence nitrogen-use efficiency and environmental quality. The chapter discusses different nitrogen fertilizers, including ammonium sulphate, ammonium chloride, ammonium nitrate and slow-release fertilizers. Nitrification inhibitors and strategies for efficient fertilizer use are also considered. Special attention is given to leaching of urea-N, nitrogen-use efficiency and nitrogen balance in the plant–soil system. The chapter therefore emphasizes balanced nitrogen management for sustaining productivity while reducing nutrient losses

Phosphorus is essential for plant growth and is involved in important physiological processes, but its availability in soil is strongly influenced by soil chemical conditions. This chapter provides a systematic treatment of phosphorus management in irrigated soils. It begins with the functions of phosphorus and the classification of soil phosphorus into organic and inorganic forms. The behaviour of phosphorus in alkali soils is discussed along with phosphate fixation, which can substantially influence phosphorus availability to crops. The chapter examines the sources of soil phosphorus used by plants and the major types of phosphatic fertilizers used in agricultural production. Available and total phosphorus are distinguished, providing a basis for assessing soil phosphorus status. The behaviour of phosphate fertilizers after application is considered in relation to their efficiency and crop uptake. The residual value of phosphatic fertilizers is also discussed, highlighting the continuing contribution of applied phosphorus to subsequent crops. Overall, the chapter emphasizes efficient phosphorus management to improve nutrient availability, fertilizer-use efficiency and sustainable crop production in irrigated soils.

Potassium is an important plant nutrient that influences water relations, carbohydrate and nitrogen metabolism, crop quality and resistance to environmental stresses. This chapter examines potassium behaviour and management in irrigated soils. It begins with the functions of potassium and explains the different forms in which potassium occurs in soil, including relatively unavailable, slowly available and readily available forms. Potassium fixation and release are discussed in relation to soil colloids, temperature, drying, soil pH and aeration. These processes determine the amount of potassium available for plant uptake and are particularly important in intensively cultivated irrigated soils. The chapter also considers luxury consumption and interactions between potassium and other elements. Potassium management is discussed through appropriate rates and methods of application and selection of suitable potassic fertilizers. The effects of potassium nutrition on plant behaviour, water utilization, carbohydrate and nitrogen metabolism, crop quality, disease resistance and low-temperature injury are highlighted. The chapter therefore provides a framework for maintaining potassium availability and preventing nutrient depletion in productive irrigated

Secondary nutrients are essential for balanced plant nutrition and sustained soil fertility in intensively cultivated irrigated systems. This chapter focuses on calcium, magnesium and sulphur, examining their sources, behaviour, availability and management in soil. Calcium is discussed in relation to its sources, fate in soil, crop removal, leaching and factors affecting its availability, including high sodium content, parent material and interactions with other cations. Calcium fertilizers and their practical importance are also considered. The chapter then examines magnesium, including its sources, behaviour in soil, uptake by crops, leaching and fertilizer management. Sulphur receives detailed attention through discussion of organic and inorganic forms, elemental sulphur and sulfides, sulphate behaviour and the different forms occurring in rice soils. Processes such as adsorption, leaching and immobilization influence sulphur availability and are therefore important under irrigated conditions. Practical aspects of sulphur management, sulphur-containing fertilizers and crop responses to sulphur fertilization are discussed, including effects on the nutritional quality of forages

Micronutrients are required in small quantities but are essential for normal plant growth and crop productivity. Their availability in irrigated soils can vary considerably because of changes in soil pH, moisture conditions, organic matter, texture and interactions with other nutrients. This chapter introduces the concepts of micronutrient deficiency and toxicity and discusses critical limits used for evaluating micronutrient status. Particular emphasis is placed on boron and zinc. Boron content, deficiency in Indian soils, availability and leaching are examined, together with the influence of soil texture, pH and moisture. Boron indicator plants, correction of deficiency, sources, crop response and frequency of application are also discussed. Interactions between boron and other nutrients receive attention. The chapter then considers zinc content and zinc deficiency in soils and examines the influence of pH, phosphate level, organic matter and adsorption by clay minerals on zinc availability. Methods, timing and rates of zinc application and crop responses are presented to support effective micronutrient management.

Successful irrigation development requires careful evaluation of soil and land characteristics before irrigation is introduced or expanded. This chapter deals with the principles and criteria used to evaluate land for irrigation and determine its suitability for sustained agricultural production. Important soil and land characteristics considered include surface-soil texture, particle-size class of the subsoil, coarse fragments, soil depth, permeability, salinity, exchangeable sodium percentage, slope and drainage. These factors determine the ability of land to store and transmit water, support root growth and withstand potential problems associated with irrigation. The chapter introduces land irrigability classification and explains the overall capability index (Ci), including its calculation and interpretation. Subclasses are considered to identify specific limitations affecting irrigated agriculture. The chapter further discusses land suitability classification and the structure used for assessing suitability. Physical condition of soil is included as an important component of land evaluation. By integrating soil, water and landscape characteristics, the chapter provides a systematic basis for identifying suitable land, recognizing limitations and planning sustainable irrigation development.

The quality of irrigation water has a direct influence on soil properties, crop growth and the long-term sustainability of irrigated agriculture. Water containing excessive salts or undesirable proportions of specific ions can create salinity, sodicity and other soil-related problems. This chapter presents the major criteria used for evaluating irrigation water quality. Salinity hazard is considered as an important indicator of the potential for salt accumulation in the soil and consequent restrictions on plant water uptake. Sodium hazard is examined because excessive sodium can adversely affect soil structure and permeability. The chapter also considers the salt index as a measure relevant to the evaluation of irrigation water. Bicarbonate hazard is discussed in relation to the chemical behaviour of irrigation water and its potential effects on soil conditions. Magnesium hazard is another important consideration in assessing the suitability of water for irrigation. By bringing these criteria together, the chapter provides a framework for evaluating irrigation water before application. Proper assessment of water quality is essential for selecting appropriate management practices and preventing long-term degradation of irrigated soils.

Increasing pressure on freshwater resources has created interest in the use of saline water for agricultural production, particularly where high-quality irrigation water is limited. This chapter examines the management possibilities associated with using saline water while addressing the risks of salinity to soil and crops. It focuses on the role of selected nutrients and soil amendments in improving crop performance under saline conditions. The roles of potassium and phosphorus are discussed in relation to plant nutrition and tolerance to salinity. Zinc is also considered for its importance in maintaining plant nutritional balance under saline conditions. The chapter further examines gypsum as an amendment and its role in managing saline soil conditions. Organic matter is discussed for its contribution to soil physical, chemical and biological properties, while biofertilizers are considered as a component of management under saline environments. The integrated use of nutrients, amendments, organic materials and biological inputs provides approaches for improving the productivity of saline soils. The chapter therefore links saline-water use with appropriate soil and nutrient management for sustainable crop production

Efficient irrigation water management is essential for achieving high crop productivity while conserving limited water resources and minimizing environmental hazards. This chapter presents the principles and practices required to manage irrigation according to crop demand and soil-water conditions. It begins with how plants obtain water from soil and explains irrigation requirements, crop water requirement terminology, water-use efficiency, field water balance and the effective root zone. Crop response to water at different growth stages is considered for important crops including rice, wheat, maize, sugarcane and mustard. Different irrigation methods are described, including surface, corrugation, sub-irrigation, sprinkler and drip irrigation. The chapter provides several approaches to irrigation scheduling based on water-holding capacity, degree of water depletion, soil-water potential, evaporation pans, leaf-water potential, canopy temperature, crop water stress index and leaf reflectance. Methods for measuring irrigation water and flowing water, including water-measuring devices and current meters, are also discussed. Scheduling based on IW/CPE ratio and depletion of available soil moisture provides practical approaches for improving water-use efficiency.

The soil–plant–water relationship integrates the major concepts of soil-water availability, root water uptake and plant transpiration into a unified system. Water movement through the soil and plant is governed by differences in water potential and by resistance within the water-conducting pathway. This chapter examines water uptake by roots and the process of transpiration, emphasizing the continuous movement of water from soil through the plant and ultimately to the atmosphere. Variations in water potential and water flux within the soil–plant system provide the basis for understanding how water is transported under different environmental and soil conditions. The resistance of the water-conducting system is considered as an important factor controlling water movement. The chapter separately discusses water movement through soil and within plants before connecting these processes with water movement from the leaf surface to the atmosphere. Control of transpiration is also examined, linking plant water relations with environmental conditions and crop water use. The chapter provides an integrated framework for understanding soil–plant–water interactions essential for efficient irrigation, crop productivity and sustainable management of water resources.